Differential type serial ports are generally used to establish links between different devices that are at relatively larger distances from one another. The European reference EP-A-0 723 352 describes an example of this type of link. Reference will be made especially to FIGS. 1, 2A and 2B and to the part of the description pertaining thereto. As explained in the reference, it is possible to perceive the appearance of an additional common mode voltage due to a difference in loads between the devices using this type of link. This common mode voltage may prompt dysfunctioning if it is outside a range of operation of a differential amplifier.
The European reference proposes an approach including offsetting the differential signals and driving two differential stages, one with the signals offset, and the other with the signals not offset. The differential stages are connected to one another by means of a wired OR connection that gives a pair of differential signals to a differential amplifier.
The device disclosed in the European reference performs relatively well when there is a common mode voltage that is of a static type or a type with low variability. However, if there is a common mode voltage that varies greatly, for example, in the vicinity of a high-frequency transmitter, a phenomenon of phase jitter is seen to appear. This is due to the difference in electrical paths between the offset signals and the signals that are not offset. This phenomenon of phase jitter is particularly troublesome when a transmission frequency in the range of one GHz is used.